But US researchers at the Massachusetts Institute of Technology say they have used spinach to harness a plant's ability to convert sunlight into energy for the first time, creating a device that may one day power laptops, mobile phones and more.

Photosynthesis, the process by which plants use light beams for energy rather than eating food like animals, has been known to scientists for decades.

But attempts to combine the organic with the electronic had always failed: isolate the photosynthetic proteins that capture the energy from sunlight, and they die.

Inject the water and salt needed to keep the proteins alive, and the electronic equipment is destroyed.

That was until Shuguang Zhang, associate director of MIT's Centre for Biomedical Engineering, discovered that protein building blocks called detergent peptides could be manipulated to keep the proteins alive up to three weeks while in contact with electronics.

"Stabilising the protein is crucial," said Zhang, who collaborated with researchers from MIT, the University of Tennessee and the US Naval Research Laboratory, including electrical engineers, nanotechnology experts and biologists.

"Detergent peptide turned out to be a wonderful material to keep proteins intact."

The scientists, whose findings were first reported by in NanoLetters, a publication of the American Chemical Society, then created a "spinach sandwich".

Why spinach?

In reality, any number of plants could have been used. But the researchers chose spinach because "it is cheap and is easily available from the grocery store", Zhang said.

The spinach was ground up and purified to isolate a protein deep within the spinach cells.

A top layer of glass was coated underneath with a conductive material and a thin layer of gold to aid the chemical reaction.

In the middle, the spinach-peptide mixture sits on a soft, organic semiconductor that prevents electrical shorts and protects the protein complexes from a bottom layer of metal.

By shining laser light on the "sandwich", researchers were able to generate a tiny current.

While one device by itself can't generate much energy, billions of them together could produce enough electricity to power a device.

"It's like a penny," Zhang said.

"One penny is not much use, but one billion pennies is a lot of money."

Practical applications are still a decade or so away, but the advantages include the technology's lightweight qualities, portability and environmental friendliness.

"There is no waste," Zhang said.

The researchers suggest the technology could be used as a backup energy supply for battery-powered portable devices.

"We have crossed the first hurdle of successfully integrating a photosynthetic protein molecular complex with a solid-state electronic device," said Marc Baldo, an assistant professor of electrical engineering and computer science at MIT.